Main Menu

The 5670kg gross weight limit to which the Lear Jet 23 had been developed proved in practice to be an unnecessary constraint. Most operators were already using two-man crews and, subsequently, CAB licensing requirements for low-capacity jet aircraft were eased. This allowed Lear to take advantage of the basic strength of the design to develop a new version, to FAR.25 standards, with a gross weight of 6123kg. Announced in October 1965, the Learjet 24 introduced among other improvements increased cabin pressurisation for operation at higher altitude.

Distinguishing a Model 23 from a 24, however, is tougher, mainly because most of the changes were internal (im-provements in the various systems) and on paper (weight and performance num-bers). The two most obvious external dif-ferences are the vortex generators-small metal tabs that project above the wing ahead of the ailerons and the windshield. A Model 23 has a set of vor-tex generators on the underside of the wing as well as the upper surface; 24s have them only on the upper surface. The Model 24's windshield, befitting a transport-category airplane, is a bird -proof design with a T-shaped stiffener on the vertical post separating the two halves; if this stiffener is missing, you are looking at a Model 23. The factory's records, in 1978, indicated that 12 of the 88 Model 23s still flying were Model 24s in every respect except serial number.)

The first Learjet 24 was flown on 24 February 1966 and gained certification the following month. In 1967 Bill Lear's holdings in Lear Jet Corporation were acquired by the Gates Rubber Company. As a result, in January 1970 the Lear Jet Corporation was renamed the Gates Learjet Corporation. A year earlier the company had started delivery of a new Learjet 24B, differing primarily by having uprated 1338kg thrust General Electric CJ610-6 engines giving an additional 100 lb thrust over the -4. The Lear 24B was certified in 1969.

Lear 24B

A lighter-weight Learjet 24C was then under development, but this was abandoned in December 1970 in favour of the Learjet 24D. This offered greater range as a result of increased fuel capacity and certification for operation at a higher gross weight. It was recognisable externally by deletion of the non-structural bullet at the junction of the horizontal and vertical tail surfaces and by having square instead of oval cabin windows. A Model 24D/A was also available with take-off weight restricted to 5669kg.

In 1976 these two versions were superseded by the Learjet 24E and Learjet 24F, introducing a new cambered wing and aerodynamic improvements to reduce stall and approach speeds. Although the two models were generally similar, the Learjet 24F differed by having almost 18 per cent greater fuel capacity. Production of the Learjet 24E was terminated during 1979, and that of the Learjet 24F during 1980, 258 model 24s having been built.

The improved model 24 with airline transport category certification was introduced, and in 1968, a stretched 10-seat model 25 was offered. This aircraft has the most exceptional climb rate in its class. The All Learjets are approved for operation at 45,000 feet, and they have much better short-field performance than is common in this category of aircraft. One reason for the climb and takeoff advantage is weight: The model 23, which needs only 2,300 feet to clear a 50-foot obstacle at gross-weight takeoff, weighs only 6,500 pounds empty and grosses at 12,500 pounds. It can fly at 26,000 feet with one engine inoperable.

Gates certified its Century III 24/25 Learjets to cruise at 51,000 feet, higher by 5,900 feet than the max for any other FAA-certified commercial aircraft. Since pressurization failure at that altitude could be fatal no matter how enthusiastic one's emergency descent were, the FAA's certifi-cation tests were the same ones they'd planned to give the abortive Boeing SST- including firing pistols point-blank at the cabin windows.